1. Field of the Invention
This invention relates generally to lighting fixtures, and more particularly to a lighting fixture illuminated by a plurality of light emitting diodes wherein the light that is within the panel is transmitted through a front surface thereof.
2. Background Art
Conventional ceiling mounted light fixtures typically employ incandescent or fluorescent light sources. Incandescent illumination systems have significant disadvantages since they consume a lot of power and produce a great deal of heat, are relatively inefficient and fragile, and require frequent replacement. Systems using fluorescent light sources also have several disadvantages since they require complicated circuitry including a ballast reactor (a coil of wire wrapped around a heavy iron core), and require substantial space for the location of the fluorescent lamps and circuitry thus increasing the profile of the fixture. Fluorescent lighting systems also consume a lot of power, are relatively inefficient, are heavy and fragile, and require frequent replacement.
Light Emitting Diodes or “LEDs” have been previously employed in the field of illuminated sign systems, and edge lighting systems, for example, luminous signs for display and advertising purposes and directional signage such as emergency exit signs. Typically, LED signs include a panel surface having graphics applied thereto or etched to define indicia and generally light is direct light from the light source onto either the viewing surface of the panel or through a translucent panel disposed behind the graphic information to be viewed. Edge lighting systems, on the other hand, use a light source to inject light into the edge of a transparent or translucent panel, whereby the panel is caused to glow and any graphics in contact with the panel are made apparent. For example, a message painted on the back side of a panel viewed from the front can be illuminated in this manner, or a panel can be caused to glow generally, the indicia being defined by or between opaque areas on the front side.
Light emitting diodes or “LEDs” are popular for use in lighting fixtures such as exit lighting primarily because of their longer service life. They also generally require lighter duty power supplies and battery backups. Maintenance costs are greatly reduced because LEDs last significantly longer before degrading to half power.
There are several patents directed toward various illuminated sign systems, and edge lighting systems employing light emitting diodes or “LEDs”.
Pulles, U.S. Pat. No. 3,892,959 discloses an edge-lighted panel having a number of light sources couple to a length of flexible wiring which is arranged to be removably affixed about the peripheral edge of the panel, with the light sources disposed within light receiving cavities in the marginal portion of the panel.
Schoniger et al, U.S. Pat. No. 5,027,258 discloses an illuminated display unit such as a board with a house number thereon or an advertising billboard, having a light guide panel. At least one electrical illuminating element is arranged in the vicinity of at least one lateral limiting edge thereof. The light guide panel serves for illuminating logo symbols, which are preferably in the form of film or of vapor coated layers, on the light guide panel. At least one of the lateral limiting edges of the light guide panel is provided with a light guide batten whose thickness is in excess of the thickness of the light guide panel and at least one of the illuminating elements is mounted in the batten. The transition between the light guide batten and the light guide panel is designed so as to have a high optical conductivity or transitivity. The external surfaces of the light guide batten are provided at least partly with an inwardly reflecting layer. This makes it possible for the light of the illuminating elements in the form of LED's with a large diameter, to be fully introduced in substantially thinner light guide panels in order to reduce costs and weight.
Hegarty, U.S. Pat. No. 5,276,591 discloses an illuminated sign system using high brightness LEDs and a translucent graphic panel with suitable opacity for the transmission of light. The graphic panel is illuminated by light from the LEDs which is injected into the edge of the graphic panel causing graphics applied to a surface of the graphic panel to become illuminated.
Tokunaga, U.S. Pat. No. 5,375,043 discloses a lighting unit of an indirect type, capable of varying the luminance and color of illumination with respect to a target to be lit, and further capable of using itself as a display unit. The lighting unit comprises a light guide plate having one side fashioned into an uneven surface or a reflective surface; a plurality of light emitting diodes for supplying a light to the light guide plate, the light derived from the diodes being dispersed through the light guide plate; and a control section which controls actions including blinking of the light emitting diodes. At least a part of the diodes is intended to emit a light different in color from that of the others so that the color or blinking of illumination can be arbitrarily varied through the control by means of the control section.
Mizobe, U.S. Pat. No. 5,641,219 discloses an illuminating device in which light is introduced mainly from a light source provided at a peripheral portion of a light emitting surface thereby illuminating the light emitting surface. The illumination of the light emitting surface is kept uniform irrespective of a shape of the light emitting surface, a type of the light source, a number of light sources and a mounting position of the light sources. The device may be used as a display device.
Tung, U.S. Pat. No. 5,842,297 discloses a luminant sign having a base including a pair of opposed casings and a image plate made of transparent acrylic resin engaged with the base. The base has a circuit board with a plurality of illuminators disposed therein. A front face and a rear face of the image plate have a number of display areas defined thereon by peripheral grooves of pictures or words. Each display area has a plurality of reflective surfaces formed therein in directions non-parallel to the beam directions of the illuminators whereby each display area of the image plate will achieve a uniform intensity.
Maas et al, U.S. Pat. No. 6,539,656 discloses a luminaire and light emitting panel comprising a relatively thin and flat light-emitting panel having a light-emitting window and, opposite the light-emitting window, a rear wall with opposed edge surfaces. At least one of the edge surfaces is light transmitting and associated with a plurality of light sources. Light originating from the light sources is spread in the panel. The device is characterized in that a plurality of deformities is provided in the panel for extracting light from the panel via the light emission window. The deformities are clustered so as to form at least one light symbol. The configuration of the clusters of deformities corresponds to the shape of the light symbol. Preferably, the luminaire has a first and a second light-transmitting edge surface, with respectively, a first and a second plurality of light sources being associated with the surfaces. A first cluster of deformities only couples light from the first light source out of the panel, thereby forming a first light symbol, while a second cluster of deformities only couples light from the second light source out of the panel, thereby forming a second light symbol, independently of the formation of the first light symbol. The luminaire provides independent lighting and coloring possibilities of light symbols in a single-panel luminaire.
Light emitting diodes or “LEDs” have not been widely accepted as a general lighting source as a replacement for incandescent or fluorescent light sources because, until just recently, they were known to have a very poor luminous efficacy and were incapable of providing sufficient brightness. As used herein, the term “luminous efficacy” means the amount of luminous flux (light) measured in lumens produced for each watt of electrical input power; and the term “efficiency” means the watts of visible energy as a ratio of the energy consumed in watts. When LEDs were first commercialized in the early 1960s, they then featured a luminous efficacy on the order of 0.15 lumen (“lm”) per watt (“lm/W”). Not until the development of isoelectronically doped indirect semiconductors in the mid-1970s did diodes become brighter and more varied in color. Red, yellow, and green diodes so manufactured could produce a luminous efficacy in the range of 1 lm/W; single heterostructure diodes raised the efficacy to a range of 2 lm/W.
The recent development and plummeting costs of new semiconductor materials have made it possible to produce low cost, “high brightness” light emitting diodes, or LEDs, that provide a new alternative to conventional filament light bulbs and fluorescent tubes as a light source in ceiling light panels. LED efficiency (watts of visible energy as a ratio of the energy consumed in watts) is advancing at a rapid rate compared to conventional incandescent and fluorescent lighting. For example, Lumileds Lighting LLC, of San Jose, Calif. produces a Luxeon™ Star line of ultra bright LEDs whose brightness exceeds previous LEDs by a factor of 5 to 10 times or even more. They can also produce a white light with a luminous efficacy in the range of up to 30 lm/W. As used in the context of the present invention, the term “high brightness LED” means a light emitting diode having a luminous efficacy of at least 30 lm/W.
The present invention is distinguished over the prior art in general, and these patents in particular by a flat planar light fixture formed of a translucent panel for the transmission of light that is illuminated by a plurality of high brightness LEDs disposed along the edges thereof. A layer of reflective material on a back surface of the panel facilitates reflection and dispersion of light that occurs within the panel through a front surface thereof. The LEDs are powered by low-voltage direct current through a rectifier and can be coupled with an emergency backup battery that is maintained in a charged condition by standard current. The light fixture may be operatively connected with a signal receiver that controls the light intensity and turns the LEDs on and off responsive to signals transmitted from a remote signal transmitter. The LEDs may be provided in different colors to allow the user to vary the color of illumination. The light fixture may also be operatively connected with an alarm system.